Brown leaf spot of cassava

Brown leaf spot of cassava is a significant fungal disease caused by the pathogen Mycosphaerella henningsii. This disease is widely distributed across tropical regions where cassava is cultivated, often leading to substantial reductions in yield due to reduced photosynthetic capacity of the plants.

The primary host for this pathogen is cassava (Manihot esculenta). The fungus infects the leaves, creating localized necrotic zones that disrupt the plant's metabolism. While it rarely kills the plant outright, the chronic infection leads to significant stress, especially in high-density plantings.

The symptoms appear as characteristic brown or dark-colored spots on the leaf surface. These spots are often irregular in shape and bounded by leaf veins. Under humid conditions, small black fruiting bodies known as perithecia develop within the necrotic spots, which are diagnostic indicators of the pathogen's presence.

Development and spread of the disease are heavily favored by high humidity, prolonged rainy seasons, and temperatures between 20°C and 28°C. The fungal spores are primarily dispersed via splashing water from rain, which spreads the inoculum from the lower canopy to the upper parts of the plant and to neighboring crops.

Management of brown leaf spot requires an integrated approach to maintain crop health. Key strategies include:

• Selection and planting of resistant cassava varieties;
• Sanitation practices, such as removing and destroying infected debris;
• Optimizing spacing to enhance airflow and reduce humidity around the leaves;
• The judicious use of protective fungicides where chemical control is economically viable.